Hitherto, in a malfunction preventive circuit for a micro-controller used to control an electronic appliance, means to prevent malfunction due to program runaway of a micro-controller is proposed, for example, in Japanese Laid-open Patent H2-176917. This means is an automatic reset circuit using a counter. Further means for preventing malfunctions induced when spark discharge occurs in a cathode-ray tube is proposed, for example, in Japanese Laid-open Patent H2-65565. This means is a circuit using a monostable multivibrator, and is intended to prevent malfunction of the micro-controller.
The conventional means, however, corresponds only to malfunctions due to program runaway of the micro-controller, and is a circuit using a counter for continuously monitoring the program or is a circuit for preventing malfunction only for spark discharges taking place in a cathode-ray tube, and is not capable of preventing malfunctions due to runaway taking place in the micro-controller.
In the event of runaway of a micro-controller in a television, usually, the user notices an abnormality on the screen, such as incorrect display, disturbed picture, or skipping of channels due to runaway and can turn off the power switch. Or, if no abnormality appears on the screen, the user may notice the abnormality only when manipulating the keys of the television. In such a case, the micro-controller is tracking abnormal actions, and when this abnormal state continues, the micro-controller may break down.
Moreover, the conventional circuit comprises a counter, multivibrator and others, and the countermeasure circuit is complicated. Thus, it does not lend itself to simplifying the parts around the micro-controller, or for saving space on the printed wiring board, and lowering the cost.